This project is evaluating the associations between individual differences in platelet oxidase activity and human behavior. Biochemical studies of different human, monkey and rodent tissues and of individual cell lines grown in tissue cultures have added further information that monamine oxidase types A and B are separate enzymes. Attempts are also being made to find and characterize more selective inhibitors of each MAO enzyme type. Studies of psychiatric, neurologic and other patient groups continue to indicate associations between reduced MAO activity and psychopathology in patients and their families. Similarly, studies in student populations have found moderately strong tendencies for certain personality features (such as sensation-seeking characteristics) and vulnerability to psychosocial difficulties (including suicide) to be associated with reduced MAO activity.